Radiation threat uncertain as blasts rock Fukushima reactors

As the devastation from Friday’s earthquake and resulting tsunami in Japan becomes apparent, the situation at the country’s Fukushima Daiichi reactor is less clear.

There was a hydrogen explosion on Saturday morning at reactor 1, followed by a similar blast at reactor 3 this morning and the extent of radiation exposure to the surrounding area it is not currently known.

The problems seems to have been caused by the tsunami, rather than the earthquake per se, which damaged the plant’s back-up diesel generators that pump water into the reactor to cool it after automatic shut down.

The Engineer will be covering the situation, but for a breakdown of how reactors are engineered to deal with seismic shaking see Friday’s coverage of the event.

The Fukushima Daiichi plant appears from a photo to be situated on the coast, but close to some hills in the background. If there is a stream in these nearby hills cooling water could be pumped to the reactor site using a ram pump that doesn’t require any electricity but simply works off a water pressure head that could be created in the stream. Just an idea.

On the Today program yesterday an admitted anti-nuclear interviewee stated than one of the Fukushima reactors in trouble was powered by plutonium, and that this element did not give off radiation that could be measured. This statement has not been challenged, but we continue to be told that radiation levels are quite low. Can anyone tell me if plutonium radiation is being measured at Fukushima?

I prefer the British AGR (Advanced Gas Cooled Reactor) design on safety to the PWR (Pressurised Water Reactor) design that we were bumped into for Sizewell B in the late 1980’s by PWR fans. The reasons:-

1) The AGR needs a couple of days to go critical and not a couple of hours like the smaller PWR.

2) Boron control rods were held in place above the AGR reactor core by electro-magnets meaning that they would be automatically dropped into place in the reactor core the moment a power failure occurred to instantly shut the nuclear chain reaction occuring in the reactor down by absorbing the neutrons emitted. Killing the nuclear reaction this also instantly kills the generation of heat in the reactor core!

3) CO2 coolant as a gas doesnt boil like water emitting steam causing gas bubbles preventing cooling water to be pumped and hence needing reactor venting to release steam and allow cooling water to fill the reactor.

That said – the fact the earthquake and subsequent hydrogen gas explosions have blown the roofs off the reactor buildings without breaching the reactors is very good testimony to the safety of the reactors themselves under such extreme conditions.

I have no idea what the fuel rods in the Fukushima reactors BUT recall that BNFL was shipping UO2 fuel pellets to Japan when the row over manual diameter and thickness checks occurred over at BNFL Sellafield on the night shift after BNFL introduced automated sizing checks like on medical tablets but left the manual checks in place. Dimension checks to ensure that the UO2 fuel pellets actually fitted inside the fuel rods that they were top fill.

UO2 fuel pellets do not contain Plutonium when manufactured and charged into a reactor BUT some of the Uranium in the Uranium Dioxide (UO2) pellets will become Plutonium as a result of the Nuclear Chain Reactions occuring in the reactor. The Plutonium formed will be contained within the UO2 pellets in the fuel rods – probably as Plutonium Dioxide and removed when the fuel rods are reprocessed meaning no plutonium emissions can occur unless the reactors themselves explode like at Chernobyl

The AGR’s were designed to make a Chernobly like explosion impossible and so far the PWR’s at Fukushima are holding up very well giving me more confidence in the PWR than I had BUT not as much as I have in the inherent safety of the UK’s AGR’s.

To answer the question on plutonium, I’ve read that one of the reactors is fuelled with a mixed uranium-plutonium fuel, both in the form of oxide pellets which are greatly prefereable tyan the metalswhichare pyrophoric.
Due to its long half life, plutonium is a fairly weak alpha emitter. However alpha particles are strongly ionising hence can be detected readilly.

Unless the incident worsens significantly, release of the uranium and/or plutonium is unlikely fuel. If it is released, plutonium is extremely radio-toxic and there is no real counter-measure to avoid uptake into the body such as in the case of iodine tablets to avoid radio-active iodine uptake.
Lets hope the engineers onsite can bring things under control despite the incredibly tough conditions under which they are working.